[Simh] Hardware fidelity in the VAX family simulators

[Bob Supnik]

First, congratulations to Mark for running the current Ultrix 750 
problem to earth.

Second, a brief diatribe about the need for fidelity to the hardware in 
the VAX simulators, which is (on the face of it) lacking outside the 
3900 and 780 simulators.

I have preached and documented the need for reasonable fidelity to 
hardware in implementing simulators. The papers on the SImH web site are 
filled with examples of minute details gumming up software behavior if a 
simulator gets them wrong. It looks to me like the 750, 730, 8600 are 
cut-and-paste jobs on the 780, and the MicroVAX I and II on the 3900. I 
admit there are strong family resemblances and, in some cases, reuse of 
hardware (the 8600 uses some of the 780 IO adapters), but as Ultrix 
proved, running VMS is an insufficient proof of correctness. Without 
reading (and implementing) the gory details of all the system-specific 
hardware, something is going to break. And if the goal is just to run 
VMS, why bother with variant models? The 780 and 3900 between them cover 
the complete history of VAX/VMS, Ultrix, and all the BSD variants.

While the 750 now runs Ultrix, will it run the next OS it is given? Even 
with the current fix, there are multiple errors remaining in the UBA. 
The 730 won't boot Ultrix off the RB80; and so on.

So my challenge to the community is twofold. First, is there more 
documentation on the variants available somewhere? I haven't found 
microcode sources or listings for the 750, 730, MicroVAX I, or 8600, for 
example. Second, are people prepared to "adopt" a model, read its 
documentation, and clean it up?

End of diatribe.

/Bob